The present invention relates to a dazzle-free reflection mirror which is capable of electrically changing reflectivity of light by the use of liquid crystal. The dazzle-free reflection mirror according to the present invention may be used mainly as a rear view mirror of an automobile, for example, and advantageous in preventing a driver from being dazzled by a head light beam of the following automobile at night or by the reflection of the sun light being incident from the rear of the vehicle in the daytime.
As a dazzle-free reflection mirror which prevents dazzling of a light by electrically changing the reflectivity of the light, it has been known that a liquid crystal cell is provided in front of the reflection mirror layer, an electric voltage is applied to the liquid crystal cell to control orientation of the molecular axis of the liquid crystal, and the intensity of light reflected by the reflection mirror layer at the rear side of the liquid crystal cell is controlled by changing the transmittivity or the absorption of light transmitted through the liquid crystal cell. As this liquid crystal, N-type nematic liquid crystal which provides dynamic scattering, a twist-nematic liquid crystal or guest-host liquid crystal which controls polarization of light is used.
However, in the dazzle-free reflection mirror using the dynamic scattering effect is disadvantageous in that the mirror surface turns white and picture image on the mirror surface cannot be recognized with ease because of dynamic scattering under dazzle-free condition.
The dazzle-free reflection mirror using the twist-nematic or guest-host type liquid crystal uses a polarizer or an analyzer to control polarization of light. For this reason, under non-dazzle-free condition, the polarized light only in one direction is reflected and the picture image on the mirror surface becomes dark, the image is distorted in dependence on the angle the driver sees the mirror, and the visible angle in which the image can be recognized on the mirror surface is narrowed.
To overcome the above-described disadvantages in the prior art, the present inventors have suggested a dazzle-free reflection mirror which has a liquid crystal mixed with dichroic pigment having optical anisotrophy so that scattered light may be absorbed by the dichroic pigment ITO U.S. application Ser. No. 561,921 , filed on Dec. 15, 1983,now abandoned. However, the reflection mirror having DSM (dynamic scattering mode) liquid crystal mixed with dichroic pigment as described in the above patent application is a current injection type and, therefore, it is likely that the pigment is deteriorated by the current and operation characteristic of the reflection mirror is deteriorated. In addition, since the molecular axis of the pigment is oriented at randam due to random orientation of the liquid crystal molecules, efficiency of absorption of light scattered by the liquid crystal molecules is low and more pigments to be mixed are necessitated.